What is the difference between diffusion and active transport?

Diffusion is the movement of particles from a high concentration to a low concentration. This process does not require energy. An example of diffusion is oxygen moving from the airways to the lungs - there is very little oxygen in the lungs but lots in the air.Active transport is the movement of particles from an area of low concentration to an area of high concentration. This process requires energy (ATP). An example of this is when plants take up nutrients from the soil. The soil does not have a large concentration of nutrients, but the plant does (because it has taken so much up) so it uses energy to take up more nutrients.